This invention relates to apparatus for driving a capstan and take-up reel rotatably mounted in a cartridge.
Ribbon or tape cartridges normally employ a supply reel for holding a supply of fresh ribbon, a take-up reel about which the used ribbon is gathered and a capstan-pinch roller arrangement for providing a pulling force for withdrawing the ribbon from the supply reel transporting the ribbon at a constant rate past a work station, such as a print platen or the like, and retracting the ribbon back into the cartridge so that it may be accumulated on the take-up reel. In a fresh cartridge, the radius of the quantity of ribbon wrapped about the take-up reel is at a minimum. As the ribbon is payed out from the supply reel, translated past the work station, retracted into the cartridge and gathered about the take-up reel, the radius of the quantity of ribbon wrapped thereabout increases until the entire quantity of ribbon has been removed from the supply reel, after which the cartridge is discarded or the ribbon is rewound about the supply reel for re-use.
In cartridges of the above type, means must be provided for driving the take-up reel as well as the capstan, in order that the ribbon may be progressively accumulated on the take-up reel without snarling. Care must be taken, however, to ensure that the rate at which ribbon is gathered onto the take-up reel does not exceed the linear at which the ribbon is drawn into the cartridge by the capstan-pinch roller assembly. If this rate is exceeded, the take-up reel drive exerts a superior pulling force on the ribbon, which is highly undesirable in most applications. This criterion, however, is not easily met, since the rate at which the ribbon is gathered on the take-up reel is not uniform but increases as the radius of the reel plus accumulated ribbon. Efforts to date to design a simple, effective and economical cartridge drive mechanism which provides a constant rotational driving force to a cartridge capstan and a variable rotational driving force to a cartridge take-up reel have not met with wide success.